ISO Standards - A point of reference for process-colorscreen printing?

Being able to produce high-quality, four-color-process graphics is a hard-won skill for any screen shop. With hundreds of potential variables poised to disrupt the process and each customer using a different benchmark to assess print accuracy, every shop tends to wander its own path to successful process-color printing. As a result, it's nearly impossible to find any two screen operations that print process color in the same fashion or achieve matching results when presented with identical jobs.

While most competing imaging methods use normalized procedures and industry-accepted tolerances to guide them through each step of the print procedure, graphics screen-printing operations usually rely on instinct and trial and error to establish the production criteria for a job. What's worse, the criteria and procedures are likely to change with each and every job they print.

This inconsistent approach to image reproduction inspired researchers and screen printers from around the world to collaborate on standards for process-color screen printing. Published by the International Organization for Standardization (ISO), the standards set tolerances and targets that screen printers should meet in each stage of production when creating process-color graphics. This article will retrace the evolution of the current standards, identify what experts perceive to be their benefits and drawbacks, and probe the rationale of adopting the standards in your own operation.

Background

There are two active ISO standards for process-color screen printing and one for screen printing in general. The first process-color standard deals with quality measurement and control when producing proofs and production prints on flatbed or cylinder graphics screen-printing presses. The second offers specifications for the color attributes and transparency level that process-color screen inks should possess. The final standard establishes internationally accepted terminology for describing the tools and activities involved in process-color screen printing.

The foundation of the standards was laid in the UK around 1990 by Bill Appleton, then a lecturer and screen-printing instructor at the Gloucestershire College of Arts and Technology, Gloucester, UK. Frustrated by the lack of available information on process-color graphics screen printing, Appleton determined that a standard for the printing method was necessary. "I realized that if you had a standard, you at least had a starting line and reference points," recalls Appleton, now a screen-printing consultant at Au-totype Int'l, Wantage, England. "The industry at that point was very secretive in the UK. Any time there was a technical article with key information, the key information was left out!"

Hoping to launch an initiative to develop standards for process-color screen printing, Appleton approached the Screen Printing Association UK (SPA) and shared his thoughts. The organization suggested he get a team together to investigate the possibility, and the British standardization project was born. (For more information about the project, see "From Confusion to Control: Developing ISO Standards for Process-Color Screen Printing," Screen Printing, July 1995, page 22). "A lot of people thought [we] couldn't develop a standard for screen printing," Appleton says, "But within the first six months, we had [support from] every major British ink manufacturer, stencil company, and supplier."

A few years later, researchers from the University of Wales Swansea, Wales, UK, threw their own experience behind the project. Dr. Timothy Claypole, director of the university's Welsh Center for Printing and Coating, notes that interest in standards development grew, "because it was felt that if you wanted to improve graphics screen printing, you had to be able to understand it. You couldn't understand it if you didn't know what you were aiming for."

In 1994, after conducting numerous tests, taking more than 1000 measurements from process-color prints generated by British shops and other sources, and defining dot-gain curves, tone-correction curves, and smallest printable dot sizes, the team printed its first job using what is referred to as an embryo standard. "We then submitted what we felt was a UK standard to the British Standards Institute," Appleton says. Because of Great Britain's membership in the European Union, which was striving for uniform standards in all member states, the Institute requested that the researchers submit their standard for evaluation to DIN, the German Institute for Standardization.

When members of the UK team approached DIN with their work, they learned that the Germans had been working on similar standards for almost eight years. "They didn't really want to publish our results over and above the German team's results, so we decided to go international," Appleton explains.

The SPA then stepped in to help usher the standards work to an international level. The organization confirmed that, even though some refinement was necessary, the team's work constituted the foundation of a standard. The SPA also informed the team that its research would need to be placed in the public domain as part of the process of presenting it to the international standards community--notably TC 130, the ISO technical committee responsible for graphic technology. "Were we willing to take the risk of ISO rejecting it? Of course we were," Appleton says. He explains that the international team not only accepted the draft standard, but also invited the UK team to its next meeting.

Cooperation

A TC 130 committee meeting, held in Berlin in the autumn of 1994, presented the first great opportunity for progress. There, members of the UK team got the chance to sit down and share their findings with representatives of the German standards team. "We thought it would be quite heavy-going," Appleton recalls. But he notes that there were no conflicts, because the UK data dealt with capillary stencils and cylinder presses, while the German research focused on direct-emulsion stencils and flatbed presses. "We absolutely dovetailed," Appleton exclaimed. "There was no friction at all!"

Within the next year, standards-research teams from countries such as Japan, Brazil, Germany, the UK, and the US met to compare notes. Dutch Drehle, senior technical associate at the Screenprinting and Graphic Imaging Association Int'l (SGIA), Fairfax, VA, recalls, "Each one was doing some kind of research on four-color process. In some cases, we were pretty close. In some cases, we were pretty far apart. So we discussed and negotiated and got those [parameters] to within the limits of what everybody could live with."

The standards

Before you get the notion that the standards for four-color process printing are there to put out your fires, it's important to remember that they only define tolerances, acceptable ranges, values, and benchmarks. A single standard may encompass several related subjects, so some ISO standards are split into several sections. This method of organization allows interested individuals to purchase only the documentation they need (standards are sold as paper-based documents and PDF files) and helps reduce their research to relevant topics. Here is an overview of each standard.

ISO 2846-4:2000 This standard is divided into sections for sheet-fed and heat-set web offset lithographic printing, cold-set offset lithographic printing, publication gravure printing, and screen printing. Standards for flexography and digital printing are under development. As Drehle explains it, part four of this standard--screen printing--specifies the color and transparency to be produced by a process-color ink set, including extender, intended for four-color process printing. The standard also describes test methods to ensure conformance. As Claypole puts it, "It specifies the point in color space that the ink should be able to pass close to. It also specifies how close it should pass--within what tolerance."

ISO 2846-4:2000 applies to screen-printing inks for conventional drying and radiation (UV) curing. It specifies L*a*b* values and density requirements, but does not address pigments or spectral reflectance. In other words, printers may be able to use inks with different pigment combinations and still achieve the standard's colorimetric requirements. They also may use their preferred printing materials to meet the standard's density specifications.

ISO 12647-5:2001 Part five of ISO 12647 is dedicated to process control for four-color process screen printing. Subjects include tone-value ranges, tone-gain curves, screen frequencies and angles, dot characteristics, gray-balance control, film-positive transmission density, and more. The standard specifies minimum acceptable tolerances and establishes target values that printers should optimally be able to achieve. In order to ensure that film positives and prints meet the standards, separations and prints must be produced along with halftone test strips (Figure 1). Printers measure the control strips using densitometers to assess dot size and spectrophotometers to measure color attributes. The measured values are used to adjust for dot gain (Figure 2) and other parameters that fall outside acceptable tolerances. "On each print, you'd have a test bar with halftone patches, and that would be to give you quality assurance," Claypole says. "You'd also need to identify the tone-gain curves for your press, which you would also want to do by producing test prints."

This standard also helps establish a common language between vendor and customer, and it offers protection to both when they agree on parameters specified within. "If a printer is going to print to the standard, and he does achieve it, then he can quantify whether the standard has been achieved or not--whether dot size is right or density is right. You can measure it and then you undercut any argument," Appleton explains. "If the job is printed as agreed, the customer can't turn around and pick some sort of fault with it out of the air to try to knock the price of the job down. It's a legal help for the printer and the customer."

ISO 12637-5:2001 The other active standard for screen printing is ISO 12637-5:2001, which addresses multilingual terminology for the printing method as a whole, rather than focusing solely on four-color process printing. The standard establishes acceptable technical language on an international level, which is essential, Appleton explains, because the meaning and context of printing terms can vary from country to country. And purchase orders, regarded as legally binding contracts in some parts of the world, become more compatible with global business practices when they contain standardized language.

TC 130 currently is revising this standard, taking it from a structure based on separate printing techniques to one that highlights production processes. The revised standard will be inclusive of all printing techniques and will include fundamental terms (12637-1), prepress terms (12637-2), printing terms (12637-3), and post-press terms (12637-4). ISO 12637-5:2001 will be withdrawn when the new standard is approved.

Perception

In the US, Drehle led the charge to collect data from the industry, including manufacturers and printers. One printer he contacted was Bron Wolff, now screen-printing technical specialist at Serigraph Inc., West Bend, WI. Wolff agreed to put the specifications in the standards to the test and help Drehle collect feedback from other printers. Wolff recalls that the majority of the screen printers he contacted told him they couldn't understand half of what the standards meant. "I could believe that because there was a bunch of stuff in there I didn't know," says Wolff.

To evaluate the standards, Wolff took inks from five manufacturers and tested them right out of the buckets, hoping to find a compliant ink set. He says he found that some manufacturers had two or three process-ink colors that fell within the ink standard's specifications, but that none of the ink producers made a full set of four CMYK inks that conformed to the standards. Another potential issue, according to Wolff, is the way inks behave. Some inks are formulated for printing on specific substrates. "The ink system that prints on vinyl might be compliant, but the ink system that prints on Coroplast--because they have to add more photoinitiators to stick to polyethylene--is probably not compliant," he explains.

When Wolff did find an ink set that came close to meeting the standards, he printed the inks on a substrate that was within specified tolerances. "Then I changed just the substrate and left everything else alone, and you know what happened? I got different prints--different colors," he says. "It was the same ink through the same screen, mesh, angle, and squeegee. Only the material changed."

A lot of four-color process work is in P-O-P and P-O-S, which involves substrates such as styrene and Coroplast. That's one reason why Dawn Hohl, technical training manager at the Screen Printing Technical Foundation (SPTF), Fairfax, VA, is concerned about the way the standards address substrates. As she puts it, "They specify around six substrates, and if you're not printing on any of those, the standard is not applicable--it isn't going to matter."

However, if a printer knows that a customer's job will be printed on a non-compliant substrate, then the two can possibly negotiate which remaining applicable parts of the standards should be met. Mike Ruff, chief technical officer at ReyHan PGF, Kansas City, MO, says dot-gain values can still be achieved. "You can meet whatever part of the standard is still there," he explains.

The lack of documented how-to information in the standards is another of Hohl's concerns. She says access to proven methods is essential for screen printers to meet the standards, because many simply aren't ready to print according to specifications. "It's a little premature for many companies. There are only a few out there who are really on the ball with four-color process," she says. "The level of understanding of measurement, what the numbers mean, and what you're actually matching--what the contract proof should be--is missing."

If printers can't understand the numbers, then there's no way to use the standards to help control the printing process or evaluate the quality of prints. "It's pretty hard to understand. The wording could be simpler, and there could be better illustrations and explanations. There are a few explanations, but not too many," Ruff says.

Participation

How many printers overseas rely on the standards for process and quality control? According to Appleton, the number is growing, particularly among shops that provide services to large, blue-chip companies. And Drehle re-emphasizes that the standards are very important to countries in Europe and Asia that include them in legally binding purchase orders.

Where does the US stand? Apparently, the standards have yet to catch on. Drehle attributes the low rate of participation to the notion that US-based companies already involved in process control would rather focus on dealing with specific printing problems than overhaul the entire printing process. Also, American printers are not compelled by law to adhere to the standards. Here are some other reasons why US shops have yet to embrace the ISO standards.

Education Industry experts in the US point to the limited number of formal training programs as one reason the standards remain out of reach to so many American printers. Unlike the UK, which provides university-level screen-printing courses that are geared toward commercial and industrial production, the US offers training programs at the college level that are limited mainly to artistic printmaking.

Beyond that, not enough US shops are even aware that the standards are available, and ones that do, according to Ruff, most often prefer to stick to current workflows and processes that produce acceptable results. Before printers can implement the standards, they need to understand what the standards actually mean and what is involved in meeting their specifications. Printers also need to know how to measure and interpret the results they achieve at each stage of the production process and how to make necessary adjustments based on those findings. Hohl says involvement from manufacturers would help create awareness, but she believes customers ultimately will drive printers to meet the standards.

Ability If you print by ISO standards, you can be color-blind and match proofs, Ruff says. But judging whether you can actually meet the standards, given your equipment, expertise, and current practices and workflows, is the first step. Can you achieve consistent tension on every screen you produce? Do you know how to use a spectrophotometer and densitometer to measure prints and separations? Wolff suggests printers work through the standards piece by piece, include their suppliers in the effort, and conduct extensive internal tests. "You need to understand the limitations of what you're doing," he says. "I don't think a lot of [printers] understand how tight these tolerances are and what is being asked of them."

Demand Wolff says that when it comes to four-color process, customers want high resolution, high definition, and color control. But at the same time, US buyers either don't know about the ISO standards or have their own quality benchmarks in mind when they walk into a print shop. The lack of consumer demand for standards compliance gives printers little incentive to set aside the money, time, materials, and manpower necessary to bring their operations up to snuff.

However, if major accounts get wind of the standards and insist printers meet the specifications, chances are that screen shops will have no choice but to tighten up their procedures or risk losing business to competitors, perhaps those using another printing method. And when printers feel pressure from valuable clients, they'll start to push ink producers toward developing compliant ink sets that will make application of the standards more effective.

Using and improving the standards

If you decide to adopt ISO standards as the basis of your production routines, be sure to document, in detail, the procedures you follow as you implement the standards and the results you get--both successes and failures. Standards are continually refined based on feedback provided by the industries in which they're used. Technical committees review the standards after no more than five years of industry use and recommend adjustments based on industry comments. In other words, your experiences could influence the way standards for screen printing are created and revised.

What is ISO?

The International Organization for Standardization (ISO) is the world's largest developer of technical standards. The standards ISO creates are designed to enhance efficiency, quality, and safety in the development, manufacture, and supply of goods and services. The standards also facilitate trade between countries, technology transfer to developing nations, consumer protection, and more.

ISO is not a government organization. Instead, it comprises a network of national standards institutes representing nearly 150 countries. ISO's members are not government-appointed delegates, even though some member organizations may be in existence by government mandate. ISO has no legal authority to enforce its standards, but various industries may make the standards market requirements. One example is ISO 9000, an international reference for quality management.

ISO's name is as unique as its structure. ISO is not an acronym; the name, pronounced eye-so, comes from the Greek isos, which means equal. The organization chose ISO because International Organization for Standardization is abbreviated differently in the world's major languages. As a result, the name ISO remains intact wherever it is used--in essence, a standardized name.

The history of ISO dates back to 1946, when delegates from 25 countries met in London to create a standards organization with an international scope. February 23, 1947 was ISO's first day of operation. Since then, ISO has relied annually on thousands of technical groups--and tens of thousands of experts within--to create the nearly 14,000 active standards in use today.

Standards are the result of voluntary efforts by members of committees and subcommittees, as well as other contributors. TC 130 is the ISO technical committee that creates standards for graphic arts, including screen printing. All standards are developed by consensus after rounds of discussion and negotiation. Vote-based approval by ISO's membership is required before the organization can publish an international standard.